The drug delivery device usually comprises a container pre-filled with a medicament for multiple injections or inhalations with a pre-determined dose. For certain applications it may be desirable to set individual doses to be delivered. The user will know which dose is set.
Existing injection devices for administering fixed doses are typically designed in one of two forms—screw thread devices and ratcheted piston devices. Screw thread devices will typically have a tolerance chain for the displacement of a single dose that runs through several components.
An example of a device for administrating an injectable product in doses is described in U.S. Pat. No. 6,837,876 B2. The device includes a casing, a reservoir for the product, a piston, an advancing element which moves the piston a selected path length, and a dosing mechanism including a number of dosing bodies and a dosing element operable to move the dosing bodies, wherein the path length is selected by the dosing element moving at least one dosing body between the piston and the advancing element.